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Baseball: The
Crack
(or Thunk) of the Bat. |
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Reprinted
from August 27, 2001 Newsweek
Source: Robert Adair
Research By Josh Ulick |
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To baseball fans, the sharp crack of
the bat is one of the sweetest sounds of the game (at least if your team
is up). But to an outfielder, that sound is a nightmare: it means head for
the warning track. A thunk, though, tells an outfielder to race in to
snare a fast-falling blooper. Since the ball's hang time is usually no
more than five seconds, sound clues give the fielder a crucial jump on the
ball long before he can see how far it's going: if a ball is hit at a center
fielder playing 300 feet deep, one that will take five seconds to land 50
feet in front of him has an almost identical trajectory in its first two
seconds as one that will take 4.3 seconds to land 50 feet behind him and
one and one that will take 4.6 seconds to drop into his glove if he stays
put. "If an outfielder waits until he can visually tell where the
ball will land, that takes almost two seconds," says physicist Robert
Adair of Yale University, who unveiled his study of bat sounds at a
meeting this summer of the Acoustical Society of America. Two seconds can
spell the difference between a put out and a hit.
What determines the sound? A wooden baseball bat is
(trust us) not that different from a guitar string. When struck almost
anywhere, it vibrates energetically, at a fundamental frequency of 170
cycles per second. "A lot of energy's lost in that vibration,"
says Adair, the National League's official physicist in the late 1980's.
The energy-sapping vibration can hurt the hitter's hands. It also leaves
less power for the bat to transfer to the ball, and it makes a sullen
thunk- the sound of a ball that's staying in the park.
If the bat connects near its sweet spot, however, it
vibrates very little, much as a tennis racket feels solid if you hit the
ball on the racket's sweet spot. In the bat, that magic spot is called a
node; hitting the ball there produces virtually no energy-sapping bat
vibrations. The "crack" is the sound of air being expelled from
between bat and ball. The ideal place to hit the ball, concludes Adair, is
where three nodes cluster, in the fattest part of the bat. With a bat
speed of 70mph, an 85mph pitch smacked near a node will sail 400 feet,
good for a home run almost everywhere but straightaway center. A ball hit
a mere five inches down the handle will be an easy 310-foot fly out. |
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